1. Field of the Invention
The present invention relates to the field of polysulfone polymers, the use of polysulfone polymers in light-transmissive environments, the use of polysulfone polymers in light-transmissive environments where the absence of spurious color is important, and the use of polysulfone polymers in lenses, such as ophthalmic lenses, sports lenses, piano lenses, protective lenses, eye shields, and the like.
2. Background of the Art
Polysulfone polymers have provided a commercial alternative to other transparent polymers for many years. Polysulfones are usually described as a generally clear, rigid, thermoplastic polymer with a glass transition temperature of about 180xc2x0 C. to about 250xc2x0 C. Polysulfones can be generally described as containing backbone aromatic rings, which are linked, preferably para-linked, partly by sulfone groups (xe2x80x94SO2xe2x80x94) and partly by dissimilar groups such as an ether linkage or hydrocarbon group (such as an alkyl or alkylene group, or a single bond. In general, the repeating units of a polysulfone may be represented generally by structures as follows:
Emxe2x80x94[(Arn)D]pxe2x80x94(Ar)Em
and/or
Ar(E)mxe2x80x94Dxe2x80x94Ar(E)m
where Ar is a 6 to 20 carbon aromatic radical (substituted or not), preferably phenylene;
D is (a) a divalent radical, of which all or different portions can be (i) linear, branched, cyclic or bicyclic, (ii) aliphatic or aromatic, and/or (iii) saturated or unsaturated, said divalent radical being composed of 1 to 35 carbon atoms together with up to five oxygen, nitrogen, sulfur and/or halogen (such as fluorine, chlorine and/or bromine) atoms; or (b) a divalent S, SO2, SO, O or CO radical; or (c) a single bond;
each E is independently hydrogen, a halogen (such as fluorine, chlorine and/or bromine), a C1 to C12, preferably C1 to C8, linear alkyl, branched alkyl, cyclic alkyl, aryl, alkaryl, aralkyl, alkoxy or aryloxy radical, such as methyl, ethyl, isopropyl, cyclopentyl, cyclohexyl, methoxy, ethoxy, benzyl, tolyl, xylyl, phenoxy and/or xylynoxy; or a nitro or nitrile radical; m is 0 or 1; and n is from 1 to about 3, and p is from about 1 to about 500. Preferably, D is a single bond or a divalent hydrocarbyl radical, preferably composed of 1 to 10 carbon atoms, and is preferably isopropylidene. Preferably, each E is independently hydrogen, a halogen, a C1 to C8 alkyl, alkaryl, aralkyl, or aryl radical.
In preferred polysulfones according to the formula above,
Ar(E)4xe2x80x94SO2xe2x80x94Ar(E)4Oxe2x80x94
represents a remnant of a bis(4-halophenyl)sulfone (e.g., bis(4-chlorophenyl)sulfone) or a sulfone-bridged bisphenol (e.g., bisphenol S) and
Ar(E)4xe2x80x94[DAr(E)4]mOxe2x80x94
represents a remnant of an optional dihydric compound, preferably 2,2-bis(4-hydroxyphenyl)propane, which is also known as bisphenol A.
Preferred polysulfones are commonly prepared from a bis(4-halophenyl)sulfone and a second, optional dihydric compound, such as bisphenol A, in a dipolar aprotic solvent such as dimethyl sulfoxide or 1-methyl-2-pyrrolidinone. A chloride or bromide may be used as the bis(4-halophenyl)sulfone monomer. Another variety of polysulfone is synthesized from a bisphenol that contains a sulfone bridge (e.g., bisphenol S). The polysulfone component used in the compositions is distinguished from a sulfone-containing polycarbonate in that such polysulfone does not contain carbonate moieties. Of course there may be blends of polysulfones or copolymers of polysulfones with carbonate linkages.
Some examples of polysulfones that are commercially available are Victrex(trademark) polyether polysulfone from ICI Americas, Inc.; Udel(trademark) bisphenol A polysulfone from BP Amoco Polymers, Inc.; Radel(copyright) A polyarylethersulfone from BP Amoco Polymers, Inc.; and Radel(copyright) polyphenylsulfone from BP Amoco Polymers, Inc.
Other bisphenols, in addition to or as an alternative to bisphenol A, which can be used with the sulfone monomer to prepare a polysulfone polymer include but are not limited to bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)oxide, bis(4-hydroxyphenyl)methane, 2,2-bis(4-hydroxydiphenyl)perfluoropropane, 1,1-bis(4-hydroxydiphenyl)cyclohexane, 4,4xe2x80x2-dihydroxybenzophenone, and 4,4xe2x80x2-dihydroxydiphenyl, and substituted counterparts.
Blends of the polysulfone polymers with aryl fluorene carbonate polymer, as shown in U.S. Pat. No. 5,340,480, are known in the manufacture of transparent elements. These blended polymers may have a composition that results in a refractive index of less than about 1.675, preferably less than about 1.670, more preferably less than about 1.666 and at least about 1.600, preferably at least about 1.610 and most preferably at least about 1.615 when measured at about 23xc2x0 C.
One class of polysulfones particularly suitable for use in transparent compositions, such as those compositions according to the present invention, desirably have a weight average molecular weight of at least about 10,000, preferably at least about 25,000, more preferably at least about 35,000, and most preferably up to about 200,000 or more. Suitable melt flow rates as measured in grams per 10 minutes by ASTM D1238, (343xc2x0 C., 8.7 kg) range from at least about 1, preferably at least about 2, and more preferably at least about 3, up to about 30, more preferably up to about 20 and most preferably up to about 10.
U.S. Pat. No. 5,511,985 describes a method of manufacturing a polysulfone resin film using the solution casting method wherein a solution of polysulfone resin using at least one solvent is chosen from among anisole, dioxane or tetrahydropyran. Other solvent combinations, such as manufacturing a polysulfone resin film with a solvent chosen from among acetone, 2-butanone, ethyl acetate, toluene and phenol is mixed in the anisole solution, dioxane solution or tetrahydropyran solution of polysulfone resin are also known.
Although the physical and chemical properties of polysulfones and polycarbonates are similar, polycarbonates have achieved a much broader commercial utility. The reasons for this disparity in commercial use is based in part upon the greater convenience of the carbonate reagents versus the sulfone reagents as well as subtle differences in manufacturing capabilities and relatively minor differences in physical properties. One of these minor differences in physical properties is a lack of color consistency or a tendency of the polysulfone polymers to display yellow tones and yellow hues. In spite of the importance of this coloration in limiting the fields of utility of polysulfones in the field of light transmissive articles, there has been little reported on work to correct this problem. There is not even known to be a significant and established explanation for the discoloration.
It would be desirable to identify the nature as well as the causes of the discoloration of polysulfone resins and to provide a polysulfone resin with reduced coloration.
The removal of certain reaction impurities in the manufacture of polysulfone polymers has been found in the present invention to reduce the undesirable coloration in the final resin. Control of synthesizing reactions, manufacturing processes, and/or purification of specific ingredients assists in the removal of specific, undesirable impurities. The yellowness index, as determined by ASTM D1925 or ASTM E313, in the commercial grades of polysulfone resins has consistently been well above 1.0 for commercial polysulfone resins. The present invention provides polysulfone polymers where the yellowness index is below 1.00, below 0.75, below 0.50, and even below 0.25.